The invention of the present application is generally directed to electrophotographic imaging members, and more specifically, the present invention relates to photoconductive imaging members comprised of amorphous tetrahedral materials and an easily fabricated ground plane layer. One embodiment of the present invention envisions a layered photoresponsive flexible imaging member comprised of amorphous silicon and a ground plane comprised of hydrogenated amorphous silicon suitably doped with p and/or n components. Accordingly, thus the ground plane layer selected for the invention of the present application can be comprised of hydrogenated amorphous silicon containing therein in effective amounts dopants such as phosphorus and/or boron. The aforementioned ground plane layers can be economically fabricated, and possess desirable adhesion and stability characteristics, particularly as compared to presently known ground planes which include polymer substrates that have been subjected to pre-metallization. Also, the imaging members of the present invention can be incorporated into electrophotographic, and particularly xerographic imaging processes wherein the latent electrostatic images formed can be developed into images of high quality with excellent resolution. Moreover, the imaging members of the present invention may be economically fabricated without concerns relating to the damaging of fragile deposited metal ground planes of the prior art; possess improved adhesion and reduction of stress, important properties in achieving flexibility; are of sufficient transparency for rear illumination; and further can be selected for positively charged or negatively charged imaging modes. Furthermore, the imaging members of the present invention can be selected for xerographic printing proceses; and are also useful wherein the images formulated are rendered visible with liquid developer compositions.
Electrostatographic imaging systems, and particularly xerographic imaging processes are extensively described in the prior art. Generally, in these processes, a photoresponsive or photoconductive material is selected for forming the latent electrostatic image thereon. The photoreceptor can be comprised of a conductive substrate containing on its surface a layer of photoconductive material, and in many instances a thin barrier layer is situated therebetween to preent charge injection from the substrate, which could adversely affect the quality of the resulting image. Examples of known useful photoconductive materials include amorphous selenium, alloys of selenium such as selenium tellurium, selenium arsenic, and the like. Additionally, there can be selected as the imaging member various organic photoconductive materials including, for example, complexes of trinitrofluorenone and polyvinylcarbazole. Recently, there has been disclosed layered organic photoresonsive devices with arylamine hole transport molecules and photogenerating layers, reference for example U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Also known are amorphous silicon phoroconductors, reference for example U.S. Pat. Nos. 4,265,991 and 4,225,222. There is disclosed in the U.S. Pat. No. 4,265,991 an electrophotographic photosensitive member comprised of a substrate, and a photoconductive overlayer of amorphous silicon containing 10 to 40 atomic percent of hydrogen and having a thickness of 5 to 80 microns. Additionally, this patent describes several processes for preparing amosphous silicon. In one process, there is prepared, in accordance with the teachings of the U.S. Pat. No. 4,265,991, an electrophotographic photosensitive member which involves heating a member present in a chamber to a temperature of 50.degree. C. to 350.degree. C., introducing a gas with a hydrogen atom, providing an electrical discharge in the chamber by electric energy to ionize the gas, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstroms per second by utilizing an electric discharge while raising the temperature of the substrate thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. Although the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 100 for example, unacceptable low quality images of poor resolution with many deletions may result. With further cycling, that is subsequent to 100 imaging cycles the image quality may continue to deteriorate often until images are partially deleted.
There are also illustrated in copending applications photoconductive imaging members comprised of amorphous silicon. Accordingly, for example, there is disclosed in copending application U.S. Ser. No. 695,990, entitled Electrophotographic Devices Containing Compensated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, an imaging member comprised of a supporting substrate and an amorphous hydrogenated silicon composition containing from about 25 parts per million by weight to about 1 percent by weight of boron compensated with substantially equal amounts of phosphorus and boron. Furthermore, described in copending application U.S. Ser. No. 548,117, entitled Electrophotographic Devices Containing Overcoated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of a supporting substrate, an amorphous silicon layer, a trapping layer comprised of doped amorphous silicon, and a top overcoating layer. Additionally, described in copending application U.S. Ser. No. 662,328, entitled Heterogeneous Electrophotographic Imaging Members of Amorphous Silicon, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of hydrogenated amorphous silicon photogenerating compositions, and a charge transporting layer of plasma deposited silicon oxide. There is further disclosed in the latter copending application an interface transition gradient between the silicon oxide charge transport layer and the photogenerating layer.
Representative prior art patents that disclose amorphous silicon imaging members include, for example, U.S. Pat. No. 4,357,179 directed to methods for preparing imaging members containing high density amorphous silicon or germanium; U.S. Pat. No. 4,237,501 which discloses a method for preparing hydrogenated amorphous silicon wherein ammonia is introduced into a reaction chamber; U.S. Pat. Nos. 3,160,51; 3,160,522; 3,496,037; 3,892,650; 4,237,151; 4,356,246; 4,359,512; 4,359,514; 4,361,638, 4,365,013; 4,365,015, see column 5; 4,377,628; 4,394,415; 4,394,426; 4,397,933; 4,403,026; 4,404,076; 4,409,308; 4,414,319; 4,416,962; 4,420,546; 4,423,133; 4,443,529; 4,451,546; 4,452,872; 4,452,875; 4,460,669; 4,460,670; 4,461,819; 4461,820; 4,462,862; 4,464,451; 4,465,750; 4,471,042; 4,477,549; 4,483,911; 4,484,809; 4,486,512;4,490,453;4,490,454; and 4,491,626.
Ground planes selected for many of the modern photoconductive imaging members must be highly flexible and adhere well to supporting substrates, particularly belt type photoreceptors over many thousands of imaging cycles. One ground plane selected for the aforementioned photoreceptors is vacuum deposited aluminum. However, aluminum films suffer from the disadvantage that they are relatively soft and exhibit poor scratch resistance during the photoreceptor fabrication processing. Additionally, vacuum deposited aluminum exhibits poor optical transmission stability after extended cycling in xerographic imaging apparatuses. This poor optical transmission stability is believed to be the result of the oxidation of the aluminum ground plane as electric current is passed across the junction between the metal and the photoreceptor. Further, the optical transmission degradiation is continuous, and for systems utilizing the erase lamps, on the non-imaging side of the photoconductive belt or web, it is necessary to adjust the erase intensity every 20,000 copies.
Aluminum ground planes of the prior art have also been found to be unstable over extended image cycling with a multistructured photoreceptor. Thus, for example, the oxides of aluminum which form on the aluminum metal selected as an electrical blocking layer cna prevent charge injection during charging of the photoconductive device. When the resistivity of the blocking layer is high, the residual potential will build across the layer as the device is subjected to cycling. Also, as the thickness of the oxide layer on the aluminum ground plate is not stable, the electrical performance characteristics of a composite photoreceptor may undergo changes during electrophotographic cycling. Further, the storage life of many composite photoreceptors with aluminum ground planes can be less than one day at high temperatures and humidity greater than 50 percent, for example, because of the accelerated oxidation of the metal. Accelerated oxidation increases optical transmission, causes copy quality nonuniformity, and may ultimately result in a loss of electrical grounding capability.
Additionally, many metals or other materials, including free metal polymers, which are highly oxidatively stable, may form a low energy injection barrier to the photoconductive material when utilized as a ground plane in a photoconductive imaging member. A hole blocking layer will usually not form on these oxidatively stable layers thus rendering the devices substantially nonfunctional as photoconductive members. Further, with respect to flexible imaging members, particularly flexible amorphous tetrahedral photoreceptors, there are selected as substrates polymers which because of their insulating characteristics must be provided with a ground plane. Usually this is achieved by premetallization of the polymer substrate, thus there results increased costs and corners relating to adhesion and/or stability characteristics of the ground plane material. Photoresponsive imaging members of the present invention overcome these problems, and more specifically with the members of th epresent invention there is improved adhesion between the ground plane and the supporting substrate. Moreover, the optical properties of the ground plane selected for the members of the present invention provide sufficient transparency for rear illumination erasure; and additionally enable a reduction in the cost of the substrate selected.
Furthermore, thee is disclosed in a copending application U.S. Ser. No. 610,552, entitled Electrophotographic Imaging Member and Process, the disclosure of which is totally incorporated herein by reference, an electrophotographic imaging member comprising a substrate, a titanium metal layer contiguous to the substrate, a charge blocking layer, a charge generator binder layer, and a charge transport layer. Disadvantages associated with the titanium metal layer include, for example, high cost, poor scratch resistance during photoreceptor fabrication, and non-optimum compabitility with plasma deposited amorphous silicon with respect to adhesion and flexibility. Additionally, the aforementioned copending application is silent with respect to amorphous silicon imaging members. Prior art of interest with respect to the subject matter of the copending application includes U.S. Pat. Nos. 3,725,058; 4,439,507; 3,926,762; 3,895,944; 4,233,384; 3,484,237; 4,265,990; 4,306,008; 4,299,897, 4,439,507; 4,026,703; 4,291,110; 3,837,851; 4,286,033; 4,349,617; 4,150,987; 3,880,657; 4,123,267; 4,322,276; 4,370,360; 4,307,942; 4,358,478; 3,201,667; and U.K. No. 1,010,331.
Although the above described imaging members, particularly the amorphous silicon photoresponsive imaging members, may be useful for their intended purposes, there continues to be a need for new imaging members. Also, there is a need for improved photoconductive imaging members with sufficiently adhered ground planes which can be continuously used in a number of imaging cycles without deterioration therefrom. Further, there is a need for improved photoresponsive imaging members with ground planes of hydrogenated amorphous silicon containing dopants therein, and wherein the resulting member is humidity insensitive and not adversely affected by the electrical consequences resulting, for example, from scratching and abrasion. Moreover,there is a need for improved photoconductive imaging members with ground planes that can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to enable the continuous use thereof in repetitive imaging and printing processes. Furthermore, there is a need for a photoresponsive imaging members with ground planes that possess superior hardness characteristics enabling them to be useful for substantially an unlimited number of imaging cycles. Additionally, there is a need for flexible imaging members with ground planes that are sufficiently adhered to the supporting substrate. Furthermore, there is a need for amorphous silicon imaging members with ground planes that can be charged to either a positive or negative polarity.